Heretofore, there are disclosed the techniques with respect to a method for manufacturing a ceramic reinforced piston as enumerated hereinbelow.
In Japanese Patent Laid-open No. 128832/1977, there is described a method for manufacturing a cast product exhibiting thermal insulation properties in which a composite product is prepared from at least a part of a shaped inorganic fiber and an aluminum or magnesium alloy cast product in accordance with either a high pressure solidification casting method or a combined use of a high pressure casting method and a gravity casting method. Furthermore, in Japanese Patent Laid-open No. 93560/1983, there is disclosed a method for manufacturing a fiber composite alloy metallic material in which a fiber product is shaped so as to conform to a site upon which reinforcement is desired as well as a site which is to be cut out after its working, the resulting shaped fiber product is set at a prescribed position in a metallic mold, and then casting is effected. Moreover, there is described in Japanese Patent Application No. 22457/1987, proposed by the present inventor, a method for manufacturing a fiber reinforced composite product in which a number of cohered balls of an inorganic short fiber material which have been previously prepared are combined and formed into a predetermined shape by the use of a binder, the resulting formed material is set at a predetermined position in a casting mold, and a molten metal is poured thereinto to cast the product. In Japanese Patent Application No. 270032/1987, also proposed by the present inventor, there is disclosed a method for manufacturing a fiber reinforced composite casting product in which a shaped product having a predetermined shape is obtained from an inorganic short fiber material which has been previously deposited in the horizontal direction by the use of a binder, the resulting shaped product is set at a prescribed position in a casting mold, and then a molten metal such as an aluminum alloy or the like is poured in said casting mold thereby effecting casting.
However, the above described conventional manufacturing methods and the machines therefor relate to, as shown in FIGS. 1 and 3, such a manufacturing method wherein ceramic particles or a shaped inorganic short fiber product (13) has been previously placed at a prescribed position in a casting mold defined by a heated mold main body (2) and a heated knock-out die (4), a molten metal (14) is poured in the interior of the casting mold, whereby the molten metal (14) such as aluminum alloy or the like is caused to penetrate into the shaped product (13) while applying a pressure by means of an upper punch (3), and the molten metal is solidified to partially reinforce only the crown surface of a piston. According to this method, however, variation in a thickness A--A of the crown surface arises dependent upon slight scattering of the molten metal (14) poured. When the amount of the molten metal poured is short, pressure of the molten metal (14) is reduced so that internal defects, such as incomplete penetration of the molten metal (14) into the shaped product (13) placed in the crown surface portion, appearance of blowholes inside the resulting product and the like, easily occur. In these circumstances, such conventional methods as described above have been practiced in such a manner that, for the sake of avoiding the internal defects as described above, a somewhat larger amount of the molten metal is used to form a thicker crown thickness A--A than the prescribed thickness, and thereafter the resulting crown thickness is reduced by means of machine work to finally obtain a predetermined thickness of the crown surface. Such cutting of a crown surface in these conventional methods tends to cut out a part of the shaped product (13) which has been already reinforced, so that mechanical strength, wear resistance, heat resistance and the like of such crown surface becomes worse than expected. In addition, since the crown surface has been reinforced with short fiber ceramics or the like, machinability of the resulting product is very poor and hence, wear and tear of cutting tools are increased.
Accordingly, the present invention has been made to solve the problems in these conventional methods. In this connection, in the present invention it is noticed that a piston generally has a piston pin cavity into which the piston pin is to be inserted and such piston pin cavity is defined in the machining process after the casting process, and hence there is no problem if a portion of a piston corresponding to the piston pin cavity thereof presents a concave form, so that such concave form is utilized for absorbing scattering of molten metal poured.